In fact, in the spring of 2011, Sweden commissioned an artist to design new, QR Code-embedded currency. They subsequently decided to postpone placing the new bills into circulation for security concerns.

Good news for Sweden: The invisible QR Code is made of printed nanoscale phosphor particles that can serve as an enhanced security watermark. Nanoparticle-infused ink is both chemically and mechanically stable. Once the ink dries on a piece of paper the code could still be read even if that paper is crumpled or folded several times.

Another approach they can consider is to embed a microscopic message within the QR code that shows up as a different color under the laser. This effectively creates a code within a code which can only be seen under a microscope.

The Netherlands, however, have forged ahead with QR Codes on their currency. To celebrate the 100th anniversary of the national mint in Utrecht they printed a limited-release stamp of QR Code-designed coins. The Code resolved to a Dutch Ministry of Finance page (in Dutch).